test: group examples into per-category folders

Move examples/*.sx and their expected/ snapshots into per-category
subfolders (examples/<category>/...). Folder = leading filename token,
with ffi-objc/ffi-jni kept whole; filenames are unchanged. The corpus
runner and LSP sweep now discover each category's expected/ dir, while
issues/ stays flat. Example 1058's repo-root-relative companion import
is made file-relative. Path strings embedded in 164 snapshots were
regenerated (path-only changes). Test-layout docs in CLAUDE.md updated.

examples/modules/0757-modules-same-name-struct-self-ref/a.sx

@@ -0,0 +1,3 @@
+// Module A authors its OWN `Box` (one field `x`) — the FIRST same-name author.
+Box :: struct { x: i64; }
+a_box :: () -> Box { return Box.{ x = 7 }; }

examples/modules/0757-modules-same-name-struct-self-ref/b.sx

@@ -0,0 +1,12 @@
+// Module B authors a same-name `Box` shadow whose field SELF-REFERENCES its own
+// name (`next: *Box`). Pre-fix the self-ref resolved to A's `Box` (registered
+// first under the bare name), so `next.*.y` failed with "field 'y' not found on
+// type 'Box'". The shadow's slot is now reserved BEFORE its fields resolve, so
+// `*Box` binds to B's OWN nominal TypeId and the deref sees B's `y`.
+Box :: struct { y: i64; next: *Box; }
+b_chain :: () -> i64 {
+    tail := Box.{ y = 42, next = null };
+    head := Box.{ y = 1, next = @tail };
+    // Walk the self-referential link; reads B's own `y`, not A's `x`.
+    return head.next.*.y;
+}